1. Field of the Invention
This invention relates generally to antenna arrays and more particularly to a dipole microwave antenna system for, inter alia, monopulse radars.
2. Description of the Prior Art
In a monopulse radar system, unlike other radar systems, more than one antenna beam is utilized. The beams are offset and the signals received therefrom are combined to simultaneously provide sum and difference signals which themselves are combined in order to obtain information necessary to determine angular tracking. Conventional two coordinate (azimuth and elevation) monopulse systems employ at least two RF channels to obtain tracking error signals from the RF characteristics of the system. One such system is disclosed in U.S. Pat. No. 3,346,861, G. G. Chadwick, et al. entitled "Sum-Difference Feed Network", dated Oct. 10, 1967. The sum and difference antenna concept is additionally taught for example in U.S. Pat. No. 3,594,811, R. L. Pierrot, entitled "Sum and Difference Antenna", July 20, 1971.
Directivity for a fixed antenna array is also obtained in various fashions, an example of which is electrically switching selected antenna elements in and out of the array. U.S. Pat. No. 1,860,123, H. Yagi, entitled "Variable Directional Electric Wave Generating Device", May 24, 1932, discloses such a means by the use of two conductor portions for each antenna element whereby if both portions are connected together, their wavelength operates to reflect electric waves whereas if one portion alone is used, it will act as either a propagator or receptor of electrical wave energy. Additional examples are shown by means of U.S. Pat. No. 3,623,109, entitled "Yagi Type Multiband Antenna . . . ", Klaus Neumann, Nov. 23, 1971, U.S. Pat. No. 3,093,826, entitled "Antenna System", C. Fink, June 11, 1963, the latter disclosing the concept of multiple lobing for obtaining directivity of a beam pattern and U.S. Pat. No. 2,632,108 entitled, "Diplexer Arrangement", O. M. Woodward, Jr., Mar. 17, 1953, which discloses the concept of beam reversing.